Most polyolefins (POs) have limited operation temperature ranges due to their inherent low heat distortion temperatures (HDTs). This is driven by a low melting temperature (Tm), which results from a relatively low crystalline cohesive energy, especially when compared to engineering thermoplastics (ETPs). Another consequence of the relative “softness” of the PO crystals, compared to ETPs, is lower moduli. Thus, POs are not typically used as structural materials.
ETPs can be defined as a class of polymers that possess one or more high-performance engineering properties (mechanical, thermal, electrical, chemical-resistant, flame-retardant, etc.). Polyamide, an example of an ETP, boasts good thermal properties (e.g., HDT of Nylon™ 6, 6 is 194° C. and its Tm is 270° C.), good stiffness and tensile strength, and good abrasion resistance. Laminar polyamides additionally have outstanding barrier properties to oxygen/air. Some representative ETPs that typically have even superior heat resistance are poly(phenylene ether) (PPE, Tg of about 260° C.), which also has excellent dimensional and hydrolytic stability; poly(phenylene sulfide) (PPS, Tm of about 285° C.); polysulfone; polyimide; and poly(ether ether ketone) (PEEK). All these ETPs require very high processing temperatures (typically greater than 250° C. and in some cases greater than 300° C.). Most of them, with few exceptions, most notably PEEK and polycarbonate (PC), also suffer from poor impact strength. The processing difficulties along with their relative low toughness, especially at low temperatures, are the two main constraints that limit broader use of ETPs.
One approach to improve the processability and/or toughness of an ETP is to blend it with a “soft” polymer or glass/carbon fibers for reinforcement. For example, PPE can be blended with polystyrene (PS) at any ratio without compatibilizer, or with polypropylene or polyamide with compatibilizer, to bring down the processing temperature. However, some engineering properties are compromised, and the compatibilizer introduces additional costs. A less common approach is to covalently modify ETPs with a soft polymer such as maleated-polypropylene, either through radical reactions or thermal reactions at very high temperatures. These non-controllable reactions, in most cases under harsh conditions, give rise to poorly defined structures and morphology, gels and compromised properties.
The synthesis of graft copolymers disclosed in this invention utilizes mild catalytic Friedel-Crafts-type alkylation reactions. A wide variety of ETPs contain aromatic moieties that are capable of undergoing alkylation. Unsaturated POs, more specifically vinyl/vinylidene-terminated polyolefins (VTPOs), can be easily grafted onto the ETP backbone. This invention provides a platform for a new generation of high-performance low-cost PO-based engineering polymeric materials, combining the advantages of individual ETP and PO, overcoming their individual disadvantages, and generating additional benefits such as well-defined morphology and high stability.
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